The present invention relates generally to the art of electric motors and other electromechanical machines. More particularly, the invention relates to an improved electrostatic shield arrangement for use in an electromechanical machine.
The shaft of an AC induction motor or other electromechanical machine is often supported by bearing assemblies maintained in position by the machine housing. In one known construction, each bearing assembly is supported by a portion of the housing known as the xe2x80x9cend bell.xe2x80x9d As its name implies, the end bell is located at one axial end of the housing, and defines a hole through which the rotatable shaft freely extends.
During operation of an electric motor, capacitive coupling can often occur between the stator and rotor. Occasionally, the potential difference developed in this manner will exceed a magnitude necessary to break down insulating grease in the bearing assembly. In this case, currents may arc or discharge from the bearing balls or rollers to the outer bearing race causing xe2x80x9cpitsxe2x80x9d or other undesirable effects. As a result, more frequent servicing of the bearing assemblies may be required.
The prior art has provided electrostatic shield arrangements to reduce capacitive coupling between the rotor and stator, and consequent current discharge through the bearing assemblies. Examples of various shield configurations can be seen in U.S. Pat. No. 5,661,353 to Erdman et al., incorporated herein by reference. While these arrangements have been effective at reducing capacitive coupling, a further need exists for various novel electrostatic shield arrangements that are compatible with mass production techniques.
The present invention recognizes and addresses the foregoing disadvantages, and others of prior art constructions and methods. Accordingly, it is an object of the present invention to provide an electromechanical machine having a novel electrostatic shield arrangement.
It is a more particular object of the present invention to provide an electromechanical machine having a novel electrostatic shield arrangement that is compatible with mass production techniques.
It is a further object of the present invention to provide a novel electrostatic shield arrangement that is compact and effective.
It is a further object of the present invention to provide a novel electrostatic shield arrangement in which a grounded conductive layer is separated from stator windings by an insulative layer.
It is also an object of the present invention to provide a novel method of manufacturing a stator for use in an electromechanical machine.
Some of these objects are achieved by an electromechanical machine comprising a housing structure rotatably supporting a shaft along a predetermined central axis. A stator having a plurality of conductive windings radially spaced about the central axis is fixed with respect to the housing structure. A rotor is also provided, located radially inward of the stator and fixed with respect to the shaft.
The electromechanical machine further comprises an electrostatic shield arrangement attached to the stator and adapted to interpose the conductive windings and the rotor. The shield arrangement comprises a conductive layer separated from the conductive windings by an insulative layer of resin material. Preferably, the insulative layer of the shield arrangement is located in respective winding slots defined in a magnetically permeable core of the stator. The conductive layer preferably comprises a nonmagnetic conductive material located radially inward of the insulative layer in the respective winding slots. The conductive layer may be in electrical communication with the magnetically permeable core, and grounded thereby. The stator also includes first and second coilheads located at opposite axial ends of the magnetically permeable core. In such embodiments, the shield arrangement is further located on an inner surface of the first and second coilheads. Preferably, the conductive layer of the shield arrangement is continuously conductive along an axial extent from the first coilhead across the slot windings to the second coilhead.
In exemplary embodiments, the insulative layer of the shield arrangement comprises a cured resin, such as a glass-filled resin, applied to the conductive windings to a predetermined thickness. Preferably, the resin substantially entirely impregnates the conductive windings of the stator. Furthermore, the conductive layer of the shield arrangement may comprise a metallic paint applied to a surface of the resin. A protective top coat may also be applied over the conductive layer on an inner surface of the stator.
Other objects of the present invention are achieved by an electromechanical machine comprising a fixed stator having conductive windings located in a plurality of parallel, axially extending winding slots defined about an inner surface of a magnetically permeable core. The stator further comprises first and second coilheads located at opposite axial ends of the magnetically permeable core. A movable rotor is located radially inward of the stator.
The electromechanical machine further includes an electrostatic shield arrangement attached to the stator. The shield arrangement includes a conductive layer separated from the windings by an insulating layer of resin material. The shield arrangement is located in the winding slots as well as on an inside surface of the first and second coilheads to interpose the conductive windings and the rotor.
The conductive layer of the shield arrangement preferably comprises a nonmagnetic conductive material located radially inward of the insulative layer. Preferably, the conductive layer is in electrical communication with the magnetically permeable core and is grounded thereby.
Other objects of the present invention are achieved by an electromechanical machine comprising a fixed stator having conductive windings located in a plurality of parallel, axially-extending winding slots defined in a magnetically permeable core. A movable rotor is operative to have a magnetic flux induced therein by excitation of the conductive windings of the stator. The conductive windings have a cured resin applied thereto to yield an insulative layer of predetermined thickness between the conductive windings and the rotor. A conductive layer of metallic paint is applied to the insulative layer and thereby separated from the conductive windings. The insulative layer and the conductive layer thus form an electrostatic shield arrangement interposing the conductive windings and the rotor.
Other objects of the present invention are achieved by a method of manufacturing a stator for use in an electromechanical machine. One step of the method involves providing a magnetically permeable core having conductive windings located in a plurality of parallel, axially-extending winding slots. An uncured resin material is applied to the conductive windings in a sufficient amount to yield an insulative layer of predetermined thickness. Next, the resin material is at least partially cured. A metallic material is then applied over the insulative layer to form a conductive layer in electrical communication with the magnetically permeable core.
According to exemplary methodology, the resin material is only partially cured prior to the metallic material being applied to the insulative layer. In such cases, the resin material is finish cured after the metallic material has been applied to the insulative layer.
Often, it will be desirable to apply and partially cure the resin material more than once before the metallic material is applied to the insulative layer in order to achieve the predetermined thickness thereof.
Other objects, features and aspects of the present invention are achieved by various combinations and subcombinations of the disclosed elements, which are discussed in greater detail below.